Chronic administration decreasesthe expressionof · 2005. 5. 16. · Proc. Natl. Acad. Sci. USA87(1990) Table 1. Psychotropic drugregulation oftyrosine hydroxylase immunoreactivity

Proc. Natl. Acad. Sci. USAVol. 87, pp. 7522-7526, October 1990Neurobiology

Chronic antidepressant administration decreases the expression oftyrosine hydroxylase in the rat locus coeruleus

(depression/noradrenergic system/hnipramine/electroconvulsive seizures/fluoxetine)

ERIC J. NESTLER*, ANNE MCMAHONt, ESTHER L. SABBANt, JOHN F. TALLMAN*, AND RONALD S. DUMAN*

*Laboratory of Molecular Psychiatry, Departments of Psychiatry and Pharmacology, Yale University School of Medicine and Connecticut Mental HealthCenter, 34 Park Street, New Haven, CT 06508; and tDepartment of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595

Communicated by Charles F. Stevens, July 2, 1990

ABSTRACT Regulation of tyrosine hydroxylase expres-sion by antidepressant treatments was investigated in the locuscoeruleus (LC), the major noradrenergic nucleus in brain. Ratswere treated chronically with various antidepressants, andtyrosine hydroxylase levels were measured in the LC byinimunoblot analysis. Representatives of all major classes ofantidepressant medication-including imipramine, nortripty-line, tranylcypromine, fluvoxamine, fluoxetine, bupropion,iprindole, and electroconvulsive seizures-were found to de-crease levels of tyrosine hydroxylase immunoreactivit by40-70% in the LC. Decreased levels of enzyme himunoreac.tivity were shown to be associated with equivalent decreases inenzyme mRNA levels. Antidepressant regulation of LC tyro-sine hydroxylase appeared specific to these compounds, inas-much as chronic treatment of rats with representatives of otherclasses of psychotropic drugs, including haloperidol, diaze-pam, clonidine, cocaine, and morphine, failed to decreaselevels of this protein. The results demonstrate that chronicantidepressants dramatically downregulate the expression oftyrosine hydroxylase in the LC and raise the possibility thatsuch regulation of the enzyme represents an adaptive responseof LC neurons to antidepressants that mediates some of theirtherapeutic actions in depression and/or other psychiatricdisturbances.

Among the best studied actions of antidepressant treatmentsare their effects on the postsynaptic noradrenergic system.Thus, one of the most consistent adaptive responses tochronic administration of antidepressants, including electro-convulsive seizures (ECS), is a downregulation of the p-adrenergic receptor-coupled cAMP system (1-3). Thesetreatments have also been shown more recently to regulateadditional postreceptor sites in this signal-transduction path-way, including specific G protein subunits (4) and cAMP-dependent protein phosphorylation (5, 6). In addition toregulation of the postsynaptic noradrenergic system, adap-tive changes also occur in presynaptic noradrenergic ele-ments in response to chronic antidepressant treatment. (i)Chronic administration of some antidepressants has beenshown to decrease a2-adrenergic receptor regulation ofcAMP production in cerebral cortex (7), an effect presumedto be localized, at least in part, to presynaptic noradrenergicnerve terminals. (ii) These treatments have been found todecrease the firing rates ofnoradrenergic neurons in the locuscoeruleus (LC) (8-10), the major noradrenergic nucleus inbrain. (iii) Chronic drug administration has been shown toalter levels of norepinephrine and its metabolites in cerebralcortex in laboratory animals, as well as in blood, cerebro-spinal fluid, and urine in human subjects (see refs. 11, 12).While these findings suggest that chronic antidepressanttreatments may alter the synthesis of norepinephrine in the

brain, no consistent reproducible effect of these treatmentson the biosynthetic pathway for norepinephrine has, to date,been established.The rate-limiting enzyme in the synthesis of norepineph-

rine is tyrosine hydroxylase. Tyrosine hydroxylase is an-60-kDa protein abundant in noradrenergic and dopaminer-gic cell bodies and distributed throughout the brain in termi-nal fields of these catecholaminergic systems. Activity of theenzyme is regulated rapidly by neurotransmitters and neu-ronal activity through its phosphorylation by several types ofprotein kinase (for review, see refs. 13 and 14). More long-term regulation of the enzyme is achieved through changes inits expression, apparently at the level of gene transcription,by a variety of chronic perturbations (15-22). Such acute andchronic regulation of tyrosine hydroxylase is thought to playa critical role in modulating the functional activity of cate-cholaminergic neuronal systems in the brain.

In the present study, the influence of chronic antidepres-sant treatments on the expression of tyrosine hydroxylasewas examined in the LC. We show here that chronic admin-istration of every major class of antidepressant results in adramatic downregulation of tyrosine hydroxylase expressionspecifically in the LC. The results raise the possibility thatdownregulation of the biosynthetic pathway for norepineph-rine contributes to the molecular mechanisms through whichantidepressant treatments exert at least some oftheir multipleclinical actions.

METHODSIn Vivo Drug Treatments. Male Sprague-Dawley rats (ini-

tial weight 150-200 g) received i.p. injections of imipramine(15 mg/kg; Sigma), nortriptyline (15 mg/kg; Sigma); tranyl-cypromine (7.5 mg/kg; Sigma), fluvoxamine (15 mg/kg;Duphar, Weesp, Holland), fluoxetine (15 mg/kg; Eli Lilly),bupropion (30 mg/kg; Burroughs Wellcome), iprindole (15mg/kg; Wyeth-Ayerst), and haloperidol (1 mg/kg; McNeilLaboratories) once daily for 18 days or cocaine hydrochloride(15 mg/kg; Sigma) twice daily for 14 days. Clonidine wasgiven in the drinking water (2 ,ug/ml) for 14 days with anaverage consumption of 300 ,ug/kg per day; morphine wasadministered by daily s.c. implantation of morphine pellets(containing 75 mg of morphine base; National Institute onDrug Abuse) for 5 days with rats used on day 6; and diazepamwas administered by implantation of two sialastic capsules(containing 90 mg of diazepam; Hoffman-La Roche), a thirdcapsule on day 10, with rats used on day 21. Control animalsreceived saline injections or underwent identical surgicalprocedures but did not receive drug implantations. ECS wasadministered once daily for 1-10 days through earclip elec-trodes (35 mA, 0.3 sec); control rats were handled in the samemanner, but no current was applied. Unless otherwise spec-

Abbreviations: LC, locus coeruleus; ECS, electroconvulsive sei-zures.

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The publication costs of this article were defrayed in part by page chargepayment. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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ified, all animals were sacrificed by decapitation 18 hr afterthe last drug treatment or ECS. The above doses, durationsof treatment, and routes of administration used for thevarious treatments were those that have been shown inprevious studies to lead to chronic effects of these treatments(see refs. 11, 23-29).Immunoblotting of Tyrosine Hydroxylase. LC and substan-

tia nigra were excised from 0.75-mm-thick coronal cross-sections of brain by obtaining 15-gauge punches with asyringe needle (30). Isolated brain regions were homogenized(10 mg/ml) in 2% SDS, and aliquots (containing 25-75 ,ug ofprotein) were adjusted to contain 50 mM Tris (pH 6.7), 2%SDS, 4% (vol/vol) glycerol, 2% (vol/vol) 2-mercaptoethanol,with bromophenol blue as a marker. The samples were thensubjected to one-dimensional SDS/polyacrylamide gel elec-trophoresis (with 7.5% acrylamide/0.3% bisacrylamide in theresolving gels) and to immunoblotting analysis for tyrosinehydroxylase exactly as described (22) using a commerciallyavailable rabbit polyclonal antiserum (1:250; Eugene Tech,Allendale, NJ) and 1251I-labeled goat anti-rabbit IgG (500cpm/pul; New England Nuclear). Resulting blots were driedand autoradiographed with the use of intensifying screens(DuPont). Levels of immunolabeling were quantitated bydensitometry or by counting excised bands in a gammacounter. Levels of immunolabeling were normalized to pro-tein levels or "per punch," which contain reproducible levelsof protein (see ref. 30). In a typical experiment, six controland treated samples were analyzed on each immunoblot.Northern Blot Analysis of Tyrosine Hydroxylase mRNA.

Total mRNA was extracted from LC and substantia nigra byusing published procedures (19). Briefly, brain regions wereisolated from control and drug-treated rats and frozen at-70°C until further use. LC from five rats or substantia nigrafrom two to three rats was pooled; RNA was extracted fromthe samples (-5 ,tg) and then analyzed by Northern blot asdescribed (22, 31) by using a cDNA clone for rat tyrosinehydroxylase provided by Edward Ziff, New York UniversityMedical Center (32). The probe was 32p-labeled by a random-primer method (Amersham) to a specific activity of T109cpm/,ug. Blots were then rehybridized with a 32P-labeledcDNA clone for 18S ribosomal RNA (provided by I. Wool,University of Chicago) and, in some experiments, with a32P-labeled cDNA clone for rat dopamine P-hydroxylase (31).Hybridizations were quantitated by densitometric analysis ofresulting autoradiograms with exposure conditions within thelinear range. In a typical experiment, three control anddrug-treated samples (each representing pooled tissue asdiscussed above) were analyzed on each Northern blot.

RESULTSRegulation of Tyrosine Hydroxylase Expression in the LC by

Imipramine Treatment. Chronic imipramine regulation oflevels of tyrosine hydroxylase protein was examined in theLC by immunoblot analysis by using a commercially avail-able antiserum (see Methods). It was found that chronicadministration of imipramine (at a daily dose of 15 mg/kg)decreased levels of tyrosine hydroxylase immunoreactivityin the LC by 55-60% (Fig. 1; Table 1). Similar results wereobtained when imipramine was administered chronically at adose of 10 mg/kg (data not shown). In contrast to chronictreatment, 1 or 7 days of imipramine treatment did notsignificantly alter levels of enzyme immunoreactivity (101 +1% and 81 ± 9%, respectively, of control ± SEM; n = 4determinations).To determine whether imipramine regulation of tyrosine

hydroxylase in the LC shows some regional specificity, theeffect of chronic imipramine on enzyme levels in othercatecholaminergic neurons was examined. In contrast to theLC, chronic imipramine was found to have no effect on levels

LC SN

_ - __ .-TH

+ + Imipramine

FIG. 1. Autoradiograms showing regulation of tyrosine hydroxy-lase immunoreactivity by chronic imipramine in the rat LC andsubstantia nigra (SN). Levels of tyrosine hydroxylase immunoreac-tivity were quantitated by immunoblot analysis as described. TH,tyrosine hydroxylase.

of enzyme immunoreactivity in the substantia nigra, a mid-brain nucleus enriched in dopaminergic cell bodies (Fig. 1 andTable 1).

Next, we studied whether decreased levels of tyrosinehydroxylase immunoreactivity in the LC in response tochronic imipramine are associated with equivalent changes inlevels ofmRNA for the enzyme, quantitated by Northern blotanalysis. Fig. 2 shows that chronic imipramine treatmentdecreased levels of tyrosine hydroxylase mRNA by -45% inthe LC. In contrast, chronic imipramine had no effect onlevels of enzyme mRNA in the substantia nigra (data notshown). In some experiments, levels ofmRNA for dopaminef3-hydroxylase, another enzyme in the biosynthetic pathwayfor norepinephrine, were determined in the LC. It was found(Fig. 2) that chronic imipramine treatment had no effect onlevels of dopamine ,B-hydroxylase mRNA.

Regulation ofTyrosine Hydroxylase Immunoreactivity in theLC by Other Antidepressant Treatments. The influence of avariety of other antidepressant treatments on the expressionoftyrosine hydroxylase in the LC was examined to determinewhether the downregulation ofenzyme expression is a mech-anism common to all antidepressants. Indeed, chronic ad-ministration of every antidepressant examined in the currentstudy, which included drugs of all major classes of antide-pressant medication and ECS (one ofthe most effective formsofantidepressant treatment), decreased (by 40-70%) levels oftyrosine hydroxylase immunoreactivity in the LC (Fig. 3;Table 1). As observed with imipramine, the effect of theseother antidepressant treatments on tyrosine hydroxylaseimmunoreactivity showed regional specificity, in that noeffect on enzyme levels was observed in the substantia nigra(Table 1) and required chronic drug or ECS administration(data not shown).

Regulation of Tyrosine Hydroxylase Immunoreactivity byOther Classes of Psychotropic Drug. A number of other typesof psychotropic drug were examined to determine whetherregulation of tyrosine hydroxylase is an effect specific toantidepressant treatments. As shown in Table 1 and Fig. 3,chronic treatment of rats with diazepam, haloperidol, cloni-dine, or cocaine had no significant effect on levels of enzymeimmunoreactivity in the LC (Table 1; Fig. 3). Also shown inTable 1 is our earlier observation (22) that chronic morphinetreatment increases levels of tyrosine hydroxylase immuno-reactivity in this brain region.

DISCUSSIONThe major finding of this study is that all major classes ofantidepressant treatment decrease the expression of tyrosinehydroxylase in rat LC. Chronic, but not acute, treatment ofrats with tricyclic antidepressants, selective serotonin re-

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Table 1. Psychotropic drug regulation of tyrosine hydroxylase immunoreactivity in the rat locus coeruleus and substantia nigra

Tyrosine hydroxylaseimmunoreactivity,% control ± SEM (n)

Treatment Acute mechanism of action LC SNAntidepressant drugs

Imipramine Serotonin and norepinephrine reuptake blocker 41 ± 3 (6)* 94 ± 10 (6)Nortriptyline Norepinephrine reuptake blocker 50 ± 11 (5)*Tranylcypromine Monoamine oxidase inhibitor 36 ± 7 (5)* 93 ± 9 (6)Fluvoxamine Serotonin reuptake blocker 31 ± 9 (6)* 114 ± 19 (5)Fluoxetine Serotonin reuptake blocker 65 ± 8 (6)*Bupropion ? 59 ± 5 (4)*Iprindole ? 57 ± 14 (5)tECS ? 39 ± 7 (6)* 97 ± 23 (5)

Nonantidepressant drugsDiazepam Anxiolytic (benzodiazepine agonist) 109 ± 22 (4)Haloperidol Antipsychotic (dopamine and other receptor antagonist) 104 ± 11 (9)Clonidine a2-Adrenergic receptor agonist 119 ± 11 (10)tCocaine Monoamine reuptake blocker 102 ± 13 (10)Morphinet Opiate receptor agonist 158 ± 12 (6)* 93 9 (3)

Rats were treated chronically with the drugs or ECS, and levels of tyrosine hydroxylase were quantitated in the LC and SN (substantia nigra)by immunoblotting analysis, as described. See refs. 11 and 29 for discussion of the acute mechanisms of action of the drugs.*~P < 0.05 compared to control by x2 test.tp < 0.2 compared to control by x2 test.tFrom ref. 22.

uptake blockers, monoamine oxidase inhibitors, certain atyp-ical antidepressants, or ECS resulted in a 40-70% reductionin levels of enzyme immunoreactivity in this brain region butnot in the substantia nigra. In contrast to antidepressants, anumber of other psychotropic drugs that do not possessclinical antidepressant activity, including diazepam, haloper-idol, clonidine, cocaine, and morphine, did not decreaselevels of LC tyrosine hydroxylase; in fact, enzyme levelswere increased in response to morphine (22) and, possibly,clonidine. Thus, downregulation of tyrosine hydroxylaseexpression appears to be an effect both common to, andspecific for, antidepressant treatments.The mechanisms by which antidepressants regulate tyro-

sine hydroxylase in the LC are unclear. Based on studies ofadrenal medulla and sympathetic ganglia, levels of tyrosine

C I

TH *

hydroxylase expression are thought to reflect the physiolog-ical activity of the cells and, hence, their requirement fornorepinephrine (see 14, 18-20). The same may hold true forthe central nervous system, where various forms of behav-ioral stress or administration of 6-hydroxydopamine in-creases both LC firing rates and tyrosine hydroxylase expres-sion in this brain region (15-17, 20, 21, 33-35). Moreover,direct depolarization of LC neurons in cultured explants hasalso been reported to increase expression of the enzyme (seeref. 36). One possibility, then, is that antidepressants down-regulate tyrosine hydroxylase expression as a direct conse-quence of their inhibitory effects on LC neuronal activity. Ithas been shown that the tricyclic antidepressants and mono-

NOR ECS TCP FLU

C I

-28S

DBH -18S-18S.

- +

_ _ _-- TH

- + -+ + treatment

18S ^ ~1 8S IS'la 185

rRNA

FIG. 2. Autoradiograms showing regulation of tyrosine hydroxy-lase and dopamine ,-hydroxylase mRNA by chronic imipramine inrat LC. Levels of tyrosine hydroxylase and dopamine P-hydroxylasemRNA were quantitated by Northern blot analysis as described. Thesame blots were reprobed for the 18S ribosomal subunit, whichindicated that the lanes contain comparable RNA levels. Levels ofLC tyrosine hydroxylase (TH) mRNA, expressed in arbitrary unitsas a ratio to levels of 18S ribosomal RNA, were 1.0 ± 0.19 vs. 0.58± 0.12 for control (lanes C) vs. imipramine-treated (lanes I) rats (P< 0.05 by Student's t test), whereas those for LC dopamine ,-hydroxylase (DBH) were 1.0 ± 0.27 vs. 1.0 ± 0.21 for control vs.imipramine-treated rats (n = 3).

-_ow AW__ _4-- TH

BUP HAL DZ MS

FIG. 3. Autoradiograms showing regulation of tyrosine hydroxy-lase immunoreactivity by chronic antidepressant and other drugtreatments in rat LC. Rats were treated with the drugs or ECS, andlevels oftyrosine hydroxylase immunoreactivity were quantitated byimmunoblot analysis, as described. NOR, nortriptyline; TCP, tra-nylcypromine; FLU, fluvoxamine; BUP, bupropion; HAL, haloper-idol; DZ, diazepam; MS, morphine; TH, tyrosine hydroxylase.

7524 Neurobiology: Nestler et al.

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amine oxidase inhibitors decrease LC firing rates acutely andthat such inhibition may persist with chronic drug adminis-tration (8, 9). Similarly, chronic administration of sertraline,a serotonin-selective reuptake blocker, has been shown re-cently to decrease the spontaneous activity of LC neuronscompared with vehicle-treated control animals (10); fluoxe-tine and fluvoxamine might be expected to have analogousactions. A sustained decrease in LC firing rates woulddecrease the requirement of the neurons for norepinephrineand could trigger the decrease in enzyme expression. Indeed,the failure of some of the other compounds tested in thisstudy to decrease tyrosine hydroxylase expression in the LCis consistent with the view that sustained decreases in LCneuronal activity mediate enzyme regulation by the antide-pressants. Thus, morphine, clonidine, and cocaine, like theantidepressants, acutely inhibit LC firing, but unlike theantidepressants, substantial tolerance develops to the inhib-itory actions of these drugs with LC firing rates returningtoward normal levels after chronic drug administration (23,25, 27). The validity of this hypothesis requires furtherinvestigation.The mechanism(s) by which antidepressants produce sus-

tained decreases in LC neuronal activity and in tyrosinehydroxylase expression is difficult to understand within theframework of known acute actions ofthese drugs on the brain(see Table 1). Thus, it is generally thought that the tricyclicantidepressants and monoamine oxidase inhibitors decreaseLC neuronal activity by increasing synaptic levels of norepi-nephrine (via inhibition of norepinephrine reuptake and deg-radation, respectively) and thereby activating inhibitory a2-

adrenergic autoreceptors on LC neurons (see refs. 8, 9, 29).However, not consistent with this view, are the observationsthat inhibition of norepinephrine reuptake or activation ofa2-adrenergic receptors by cocaine and clonidine, respec-tively, does not lead to sustained inhibition of LC neuronalactivity or to decreased tyrosine hydroxylase expression.The regulation of tyrosine hydroxylase by the selective

serotonin reuptake inhibitors fluoxetine and fluvoxamine isparticularly interesting and supports the view that the sero-tonergic system exerts significant influence on the functionalstate of noradrenergic neurons (see ref. 10). It is possible thatsuch effects reflect direct actions of the drugs on serotonergicnerve terminals within the LC, where serotonin is known toinhibit LC neurons (37, 38). Alternatively, the drugs couldfacilitate serotonergic neurotransmission in some other brainregion(s) that would then indirectly inhibit LC neuronalactivity.Based on the inability of the known acute actions of

classical antidepressants (namely, inhibition of norepineph-rine reuptake and a2-adrenergic receptor activation) to ac-count for chronic antidepressant actions on the LC, it seemslikely that these treatments, as well as the atypical antide-pressants, have additional acute and chronic actions thatmediate their regulation of LC neuronal activity and tyrosinehydroxylase expression. For example, all antidepressanttreatments listed in Table 1 have been shown to alter anumber of neurotransmitter receptor systems throughout thebrain (see refs. 11, 29), indicating that regulation of tyrosinehydroxylase in the LC could be a consequence of complex,polysynaptic actions of many neurotransmitters on LC neu-rons. It is also conceivable that one or several of theantidepressant drugs regulate tyrosine hydroxylase via directactions on intracellular messenger pathways and geneexpression in LC neuronal cell bodies, actions independent ofsynaptic inputs. Support for this provocative idea comes

from recent studies on C6 glioma cells (see refs. 39, 40).Antidepressant regulation of tyrosine hydroxylase appears

to be mediated at a pretranslational level. Thus, chronicimipramine treatment was found to decrease levels of tyro-sine hydroxylase mRNA in the LC. This effect was specific

Proc. Natl. Acad. Sci. USA 87 (1990) 7525

to tyrosine hydroxylase, inasmuch as mRNA levels of do-pamine j3-hydroxylase, another enzyme in the biosynthesis ofnorepinephrine, were not influenced by this drug treatment.Decreased levels of tyrosine hydroxylase mRNA and proteinobserved in response to chronic imipramine indicate thatdrug treatment may alter levels of the enzyme through theregulation ofgene expression, although it is also possible thatthe effect of the drug occurs through changes in turnoverrates of enzyme mRNA and/or protein.Decreased expression of tyrosine hydroxylase mRNA and

protein by chronic antidepressant treatments indicates thatthe maximal capacity of LC neurons to synthesize norepi-nephrine is also decreased under these conditions. A separatequestion concerns what effect antidepressant treatmentsexert on the average catalytic activity of tyrosine hydroxy-lase. There is one report of a decrease in tyrosine hydroxy-lase activity in the LC after chronic imipramine treatment(41). Moreover, chronic administration of certain antidepres-sants has been reported to decrease norepinephrine levels incerebral cortex of laboratory animals and levels of norepi-nephrine metabolites in cerebrospinal fluid and plasma inpatients with major depression (see refs. 11, 12). However,chronic ECS has been reported to increase tyrosine hydrox-ylase activity in the LC (42). The reason for this discrepancymay lie in the fact that, despite lower total enzyme levels,enzyme activity could vary widely depending on the state ofactivation (i.e., state of phosphorylation) of the enzyme.Such lability in tyrosine hydroxylase activity would partic-ularly complicate analysis of activity in response to in vivodrug treatments, where postmortum changes could occur. Incontrast, levels of tyrosine hydroxylase mRNA and proteinwould be expected to be less vulnerable to rapid fluctuationsin neuronal activity or postmortum artifacts and, therefore,may provide a more reliable measure of the long-term regu-lation of the enzyme in response to chronic manipulations.The findings of the present study, together with earlier

evidence for decreased P3-adrenergic receptor function inprojection areas of noradrenergic neurons (1-3), indicate thatchronic antidepressant administration downregulates bothpresynaptic and postsynaptic noradrenergic function. In fact,it is striking that the same drugs that downregulate tyrosinehydroxylase also downregulate 8-adrenergic receptor func-tion. It will be important in future studies in determinewhether the two effects are in some way causally related or,rather, whether they reflect complex actions of the drugs ona number of distinct brain regions.The view that downregulation of the noradrenergic system

contributes to the therapeutic actions of antidepressant treat-ments raises the question as to whether this neurotransmittersystem is in some way involved in the etiology or expressionof certain forms of clinical depression (see refs. 11, 12).Chronic stress, which may play a role in precipitating epi-sodes of depression, leads to increased levels of tyrosinehydroxylase expression in the LC in rats (see ref. 20), aneffect blocked by pretreatment of animals with antidepres-sants (43). These findings raise the possibility that an over-active noradrenergic system could contribute to depressivesymptomatology and that the therapeutic action of antide-pressant treatments reverses such overactivity, in part, bydecreasing tyrosine hydroxylase expression in the LC. Clin-ical studies have reported that a subset of depressed patientsexhibit increased levels of central and/or peripheral norepi-nephrine and its metabolites, although the significance ofsuch alterations remains controversial, with other studiesreporting decreases or no differences in levels of centralnorepinephrine in depressed patients (see refs. 11, 12). Theresults of these various studies also indicate the possibilitythat, in a similar fashion, the noradrenergic system may beinvolved in the expression and/or treatment of a number ofmental disorders other than depression (e.g., panic disorder,

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7526 Neurobiology: Nestler et al.

posttraumatic stress disorder, eating disorders) for whichantidepressant medications are known to provide some clin-ical benefit. Further studies are needed to test these varioushypotheses and examine the role played by the regulation oftyrosine hydroxylase expression in the mechanisms by whichantidepressant treatments and stress produce their multipleclinical effects.

This work was supported by U.S. Public Health Service GrantsDA-05490 (to E.J.N.), MH45481 (to R.S.D.), and NS 20440 andRCDA NS 01121 (to E.L.S.), and by the Abraham Ribicoff ResearchFacilities, Connecticut Mental Health Center, State of ConnecticutDepartment of Mental Health.

1. Vetulani, J., Stawarz, R. J., Dingell, J. V. & Sulser, F. (1976)Naunyn Schmiedebergs Arch. Pharmacol. 293, 109-114.

2. Wolfe, B. B., Harden, T. K., Sporn, J. R. & Molinoff, P. B.(1978) J. Pharmacol. Exp. Ther. 207, 446-457.

3. Duman, R. S., Strada, S. J. & Enna, S. J. (1985) J. Pharmacol.Exp. Ther. 234, 409-414.

4. Duman, R. S., Terwilliger, R. Z. & Nestler, E. J. (1989) Phar-macologist 31, 182 (abstr.).

5. Nestler, E. J., Terwilliger, R. Z. & Duman, R. S. (1989) J.Neurochem. 53, 1644-1647.

6. Perez, J., Tinelli, D., Brunello, N. & Racagni, G. (1989) Eur. J.Pharmacol. 172, 305-316.

7. Nomura, S., Duman, R. S. & Enna, S. J. (1987) Brain Res. 410,195-198.

8. Huang, J., Maas, J. W. & Hu, G. H. (1980) Eur. J. Pharmacol.68, 41-47.

9. Blier, P. & De Montigny, C. (1985) Neuroscience 16, 949-955.10. Valentino, R. J., Curtis, A. L., Parris, D. G. & Wehby, R. G.

(1990) J. Pharmacol. Exp. Ther. 253, 833-840.11. Heninger, G. R. & Charney, D. S. (1987) in Psychopharma-

cology: Third Generation of Progress, ed. Meltzer, H. Y.(Raven, New York), pp. 535-544.

12. Gold, P. W., Goodwin, F. K. & Chrousos, G. P. (1988) N.Engl. J. Med. 319, 348-353.

13. Nestler, E. J. & Greengard, P. (1989) in Basic Neurochemistry:Molecular, Cellular, and Medical Aspects, eds. Siegel, G. J.,Agranoff, B., Albers, R. W. & Molinoff, P. (Raven, NewYork), 4th Ed., pp. 373-398.

14. Zigmond, R. E., Schwarzchild, M. A. & Rittenhouse, A. R.(1989) Annu. Rev. Neurosci. 12, 415-461.

15. Zigmond, R. E., Schon, F. & Iversen, L. L. (1974) Brain Res.70, 547-552.

16. Reis, D. J., Joh, T. H., Ross, R. A. & Pickel, V. M. (1974)Brain Res. 81, 380-386.

17. Acheson, A. L. & Zigmond, M. J. (1981) J. Neurosci. 1,492-504.

18. Tank, W. A., Lewis, E. J., Chikaraishi, D. M. & Weiner, N.(1985) J. Neurochem. 45, 1030-1033.

19. Faucon-Biguet, N., Buda, M., Lamouroux, A., Samolyk, D. &Mallet, J. (1986) EMBO J. 5, 287-291.

20. Richard, F., Faucon-Biguet, N., Labatut, R., Rollet, D., Mal-let, J. & Buda, M. (1988) J. Neurosci. Res. 20, 32-37.

21. Schalling, M., Stieg, P. E., Lindquist, C. & Goldstein, M.(1989) Proc. Natl. Acad. Sci. USA 86, 4301-4305.

22. Guitart, X., Hayward, M., Nisenbaum, L. K., Beitner, D. B.,Haycock, J. W. & Nestler, E. J. (1990) J. Neurosci. 10, 2635-2645.

23. Pitts, D. K. & Marwah, J. (1989) Eur. J. Pharmacol. 160,201-209.

24. Nestler, E. J., Terwilliger, R. Z., Walker, J., Sevarnno, K. A.& Duman, R. S. (1990) J. Neurochem. 55, 1079-1082.

25. Engberg, G., Elam, M. & Svensson, T. H. (1982) Life Sci. 30,235-243.

26. Nestler, E. J., Terwilliger, R. Z. & Beitner, D. B. (1989) LifeSci. 45, 1073-1080.

27. Aghajanian, G. K. (1978) Nature (London) 276, 186-188.28. Guitart, X. & Nestler, E. J. (1989) J. Neurosci. 9, 4371-4387.29. Cooper, J. R., Bloom, F. E. & Roth, R. H. (1986) The Bio-

chemical Basis of Neuropharmacology (Oxford Univ. Press,New York), 5th Ed.

30. Nestler, E. J. & Tallman, J. F. (1988) Mol. Pharmacol. 33,127-132.

31. McMahon, A., Geertman, R. & Sabban, E. L. (1990) J. Neu-rosci. Res. 25, 395-404.

32. Leonard, D. B. B., Ziff, E. B. & Greene, L. A (1987) Mol.Cell. Biol. 7, 3156-3167.

33. Chiodo, L. A., Acheson, A. L., Zigmond, J. J. & Stricker,E. M. (1983) Brain Res. 264, 123-126.

34. Valentino, R. J. & Curtis, A. L. (1989) Soc. Neurosci. Abstr.15, 849.

35. Abercrombie, E. D. & Jacobs, B. L. (1987) J. Neurosci. 7,2837-2843.

36. Black, I. B., Adler, J. E., Dreyfus, C. F., Friedman, W. F.,LaGamma, E. F. & Roach, A. H. (1987) Science 236, 1263-1268.

37. Chouvet, G., Akaoka, H. & Aston-Jones, G. (1988) C. R. Acad.Sci. (Paris) 306, 339-344.

38. Bobker, D. H. & Williams, J. T. (1989) J. Pharmacol. Exp.Ther. 250, 37-43.

39. Fishman, P. H. & Finberg, J. P. M. (1987) J. Neurochem. 49,282-289.

40. Broquet, P., Baubichon-Cortay, H., George, P., Peschard,M.-J. & Louisot, P. (1990) J. Neurochem. 54, 388-394.

41. Segal, D. S., Kuczenski, R. & Mandell, A. J. (1974) Biol.Psychiatry 9, 147-159.

42. Masserano, J. M., Takimoto, G. S. & Weiner, N. (1981) Sci-ence 214, 662-665.

43. Melia, K. R., Nestler, E. J., Haycock, J. W. & Duman, R. S.(1990) Soc. Neurosci. Abstr. 16, 444.

Proc. Natl. Acad. Sci. USA 87 (1990)

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